> one thing I've never understood about these kinetic launch vehicles is that, if something falls from orbit, it tends to burn up. But if we want to launch it f

> one thing I've never understood about these kinetic launch vehicles is that, if something falls from orbit, it tends to burn up. But if we want to launch it from ground to arrive at orbital altitude with orbital velocity, then we have to launch it faster than orbital velocity and from thicker atmosphere. The kinetic launch vehicles achieve orbital altitude but not orbital velocity. They require a rocket engine to accelerate them to orbital velocity. This is no different from Blue Origin flights where they get to space, but then fall back down to earth (relatively slowly). To achieve "orbital" altitude you need to start with enough kinetic energy to make it to the Karman line (100km) with zero (or more) energy left. The kinetic energy a tthe start of the trip needs to equal the potential (gravitational) energy at 100km (neglecting friction). Gravitational energy is U=mgh so, for 1kg and 100km (g = 9.8m/s^2)... U = 1e3 x 9.8 x 100e3 = 9.8e8 Kinetic energy = 1/2mv^2 so... 9.8e8 = 1/2 x 1e3 x v^2 Solving for v... v = 1,400 m/s = 5.04e3 km/h (3355mph) or roughly mach 5 (if I got all my units right) Launching a projectile at mach 5 will result in a significant amount of heat, but nothing close to the heat from orbital velocity (6.8 to 7.9 km/s => 24,840–28,080 km/h) https://en.wikipedia.org/wiki/Gravitational_energy https://en.wikipedia.org/wiki/Gravitational_energy https://en.wikipedia.org/wiki/Kinetic_energy https://en.wikipedia.org/wiki/Kinetic_energy https://en.wikipedia.org/wiki/Orbital_speed https://en.wikipedia.org/wiki/Orbital_speed